Process for the preparation of stretch resistant polypivalolactone fibers

ABSTRACT

POLYPIVALOLACTONE FIBERS WITH HIGH RESISTANCE TO STRETCH AFTER BOIL-OFF ARE PREPARED BY A CRITICAL COMBINATION OF DRAWING AND HEATING STEPS PERFORMED UPON ORIENTED POLYPIVALOLACTONE FIBERS. THESE FIBERS ARE CHARACTERIZED BY THEIR UNIQUE STRUCTURAL FORM, MOST SIGNIFICANTLY THE RELATIVE AMOUNTS OF THE POLYMER WHICH EXIST IN THE TWO CRYSTALLINE FORMS: A AND B.

Dec. 4, 1973 SHEE LUP JUNG ET AL 3,776,997 PROCESS FOR THE PREPARATION OF STRETCH RESISTANT POLYPIVALOLACTONE FIBERS Filed Dec. 5, 1966 3 Sheets-Sheet 1 INVENTOR S LAWRENCE FORWOOD BESTE 'SHEE LUP JUNG ATTORNEY Dec. 4, 1973 SHEE LUP JUNG ET AL 3,776,997

PROCESS FOR THE PREPARATION OF STRETCH RESISTANT POLYPIVALOLACTONE FIBERS 3 Sheets-Sheet 2 Filed Dec. 5:, 1966 a C D a l a 3 2|.O 6 4 |3.5 9,0

I A M ATTORNEY Dec. 4, 1973 SHEE LUP JUNG ETAL PROCESS FOR THE PREPARATION OF STRETCH RESISTANT POLYPIVALOLACTONE FIBERS 3 Sheets-Sheet 3 Filed Dec. 5, 1966 F l G..

FIBER AXIS a 4 m m G O4C\ W2.

S R O W T 5 BE MB D R m H G C RN OU FJ E w NL M E W F. A H L5 US. Cl. 264--290 1 Claim ABSTRACT OF THE DISCLOSURE Polypivalolactone fibers with high resistance to stretch after boil-off are prepared by a critical combination of drawing and heating steps performed upon oriented polypivalolactone fibers. These fibers are characterized by their unique structural form, most significantly the relative amounts of the polymer which exist in the two crystalline forms: a and B.

This invention relates to novel fibers exhibiting unusually high resistance to stretch and to a novel process for their preparation and more particularly to polypivalolactone fibers having high resistance to elongation and their preparation by a critical combination of fiber forming, crystallizing and orienting steps.

For many uses the performance of textile fibers is related to their ability to resist stretch. Fibers with high resistance to stretch (and fabrics made from them) have greater dimensional stability. Garments made from such yarns are less likely to become baggy at the knees, elbows or other points of stress. Yarns or cords with high resistance to stretch are also desirable as reinforcement for plastic products, hose, belts, tires, etc. Low resistance to stretch can lead to non-uniform drawing during the processing of staple fibers into yarn resulting in non-uniform shrinkage which can cause puckering in fabrics. These factors are also significant in fabrics containing fiber blends. Since the usual breaking elongation of cotton is 7%, a synthetic fiber should have a high tensile stress at 7% elongation to avoid weakening a fabric containing these two fibers.

A measure of the ability of a fiber to resist stretching is obtained by measuring the load in grams per denier required to elongate the fiber 7%. This measurement can be made according to the procedure of ASTM D2256- 64T and is designated herein as T Drawn polypivalolactone fibers prepared as by Alderson in his United States Patent 2,658,055 and Reynolds & Vickers in their British Patent 766,347 have a T or 1 g.p.d. or less after relaxed boil-off. Polypivalolactone fibers having a T of greater than about 1.5 g.p.d. after relaxed boil-off have been greatly desired, but up to the present time such fibers have not been obtainable.

A polypivalolactone fiber has now been produced which exhibits a T7 of about 1.5 g.p.d. and higher even after a 30-minute relaxed boil-off. The fiber which is resistant to stretching comprises a polypivalolactone fiber having a novel physical structure. The structural elements in terms of which the novel fiber is characterized are discussed fully hereinbelow, but in summary they are as follows:

(1) The molecular weight of the polypivalolactone, a measure of which is given by the inherent viscosity (as hereinafter defined);

(2) The orientation of the fiber internal structure as characterized by its orientation angle;

(3) The relative amounts of the polymer existing in the two crystalline forms of which polypivalolactone has been found to be comprised: the a crystalline form in which a sharp layer line having a 5.97 A. spacing appears on the wide-angle X-ray diffraction pattern and United States Patent 3,776,997 Patented Dec. 4, 1973 the ,3 crystalline form in which a diffuse layer line appears having a spacing of 4.74 A., a measure of the relative amounts being given by the on ratio;

(4) The apparent width of the a crystallites or the average width of ordered regions of a crystalline form across the fiber as characterized by the apparent on crystallite size transverse to the fiber axis;

(5) The apparent length variation of the a crystalline domain in the direction parallel to the fiber axis, a measure of which is given by the radial breadth of the low angle meridional X-ray peak.

Briefly described the novel fiber comprises a highly oriented polypivalolactone fiber with a limited amount of a. crystalline form and characterized by an a ratio of 1.5 or less and by the high order of length of its a crystallites parallel to the fiber axis as measured by a value of not more than 0.40" for the radial breadth of the low angle meridional X-ray peak. The novel fiber thus differs fundamentally in structure from the previously known types of polypivalolactone fibers (a) a substantially unoriented polypivalolactone fiber in the on crystalline form in which both the length and width of the a crystallites are of relatively low order and (b) an oriented polypivalolactone fiber which has a substantial degree of B crystalline structure but upon relaxed boil-off in water is converted to a predominantly a crystalline fiber, the fiber (b) being obtained by the orientation of fiber (a).

More specifically, the stretch resistant fiber of this invention comprises a highly crystalline polypivalolactone fiber having an inherent viscosity m of at least about 0.75, said fiber being highly oriented as characterized by a wide angle X-ray orientation angle of 17 or less, said fiber having a limited amount of tat-crystalline form. The a ratio as defined by the quotient of the area A of an equatorial intensity-trace of the diffraction pattern between angles of 9 and 13.5 and the area B of the intensity trace between the angles 16.4 and 21.0 being less than 1.5, the apparent 0L crystalline size transverse to the fiber axis being less than A., said fiber also being characterized by its highly ordered on crystalline character parallel to the fiber axis as measured by a value of not more than 0.40 for the radial breadth of the low angle meridional X-ray peak.

The novel fiber of the invention exhibits a T ranging from a minimum of 1.5 grams per denier to 4 grams per denier and even higher.

The fiber of this invention is produced by a novel process comprising heating an oriented polypivalolactone fiber having an inherent viscosity greater than about 0.75 to a temperature of at least C. and preferably to at least C. for at least 3 seconds (except for suitable block copolymers which do not require this step), drawing the fibers at 120-190" C. but preferably at about 140 C. to a high degree of orientation (usually 1.5- 2.0x). but preferably to the maximum draw ratio obtainable, followed by heat-setting at 200 C. (usually for about 20 minutes in an oven) to give fibers with an a ratio of 1.50 or less, an apparent on crystallite size of 125 A. or less, a low angle radial breadth of 0.40 or less, and an 11.5 orientation angle of 17 or less. The drawing may be done in one or more stages and may be carried out at the same or different temperatures within the range indicated. The heat setting may be carried out in one or more stages and. at various temperatures Within the ranges indicated.

The fibers to which the process of the invention is applied are readily prepared by conventional melt-spinning techniques with orientation of the fibers to an orientation angle having a numerical value less than 8 m +15. The required orientation may be developed during the spinning step alone simply by taking up the fibers on a forwarding roll or windup roll at a high, spin-stretch factor, i.e., with a ratio of spinning speed at windup to the jet speed of the polymer stream issuing from the capillary orifice sufficient to orient the fibers to the desired extent. The orientation of the spun fibers is readily increased (lower orientation angle) by drawing them immediately following the spinning step. Fibers which have not been subjected to a drawing step usually have a high degree of a crystalline form as indicated by a high on ratio even when they have received substantial orientation of fiber structure by spinning at a high spin-stretch factor. Drawn fibers typically have a substantial degree of B crystalline form as characterized by an ratio of less than 1.70. Heating drawn or undrawn fibers in the temperature range of 150 to 200 C. results in fibers substantially of a crystalline form as indicated by an a ratio greater than 1.70.

The conditions necessary for the preparation of the novel high T, fiber of this invention vary somewhat depending on the history of the fiber, but in general the process consists of drawing a previously heat-set fiber followed by a heat-setting treatment to stabilize the structure. Optimum results are obtained if the starting fibers are heat-set in the temperature range of 170 to 200 C. although no prior heat-setting is required of certain block copolymers. The yarn is then drawn about 1.5 to 2X but preferably to the maximum draw ratio attainable in the temperature range of 120 to 190 C. but preferably at about 140 C. The final heat-setting is accomplished in the temperature range of 160 to 200 C. The initial heat-setting, drawing, and final heat-setting may be carried out as separate steps or, by the use of suitable equipment, may be carried out on a continuous basis. The heat-setting and drawing operations may be carried out in one or more stages and at one or more temperatures. The fibers may be heat-set taut or some slight relaxation can be allowed during the heat-setting operation. The minimum heat-setting time required is about one second or less at the higher temperatures with longer heating times required at the lower temperatures. In the temperature range of 170 to 180 C., a heating time of 20 to 40 minutes is adequate. The stretch resistant properties are retained even after 30 minute relaxed boil-off. Because of their ability to resist stretching, the fibers of this invention are particularly useful in blends with cotton or other fibers having similar stress/strain characteristics. Fabrics prepared from such blends have improved strength and improved wrinkle resistance. The fibers of this invention are also useful as reinforcement for plastic products, hose, belts, tires, etc.

The discovery that oriented polypivalolactone fibers can be converted from their previously known structural forms to a new stable structural form exhibiting high resistance to stretch was highly unexpected. Previously known polypivalolactone fibers exhibit poor resistance to stretch and heat treatment of these fibers results in even less resistance to stretch. Maximum T, values for these fibers after relaxed boil-off were in the range of .9 to 1 gram per denier, while the new stretch resistant polypivalolactone fibers exhibit T, values of about 1.5 to 4 g.p.d. or even higher.

ILLUSTRATIVE DRAWINGS AND DEFINITIONS The nature of the invention will be more fully understood by reference to the accompanying drawings, in which FIG. 1 is a schematic representation of the structure of a portion of a polypivalolactone fiber, taken in cross section along a plane containing the fiber axis;

FIG. 2 is a typical X-ray diffractometer scan, or equatorial intensity trace of the X-ray diffraction pattern, of the fiber of FIG. 1, illustrating the method of determining the a ratio and the apparent on crystallite size transverse to the fiber axis;

FIG. 3 is a typical radial photometer intensity trace of a low angle X-ray diffractiqn pattern of the fiber of 4 FIG. 1, illustrating the method of determining the radial breadth of the low angle meridional X-ray peak;

FIG. 4a is a representation of a proposed conformation of two repeating units of the polypivalolactone molecule in the on crystalline form; and

FIG. 4b is a representation of a proposed conformation of two repeating units of the polypivalolactone molecule in the B crystalline form.

Turning now to the figures, FIG. 1 is a schematic representation of the structure of a portion of a polypivalolactone fiber in a plane which includes the fiber axis F. In the figure, crystallites of a crystalline form 1, are exemplified as aligned with the fiber axis F within the orientation angle 0. Crystallites of the a crystalline form, 2, are shown dispersed within the fiber material. A measure of the variation in length, 3, of the a crystallites or, ordered regions of a crystalline form parallel to the fiber axis, is given by the radial breadth of the low angle meriodional X-ray peak. The apparent a crystallite size, identified as 4 in FIG. 1, represents the width of the a crystallite transverse to the fiber axis. The structural parameters by which the fiber is characterized are illustrated schematically in FIG. 1, and quantitative values for the parameters are determined by the various X- ray procedures described in detail below. It is to be understood that the invention is defined in terms of the quantitative values for the parameters, and that the schematic interpretation of the parameters is not intended to be taken as limiting.

In the fiber of the invention, the crystalline regions of the polypivalolactone are comprised of two forms: the oc crystalline form, in which a sharp layer line having a 5.97 A. spacing appears on the wide angle X-ray diffraction pattern, and the 5 crystalline form, in which a diffuse layer line having a 4.74 A. spacing appears. A measure of the relative amount of the two forms is given by the a ratio. A suitable method for determining the a ratio involves the use of a reflection technique to record an equatorial intensity trace of the X-ray diffraction pattern with an X-ray diffractometer (employing a goniometer with a 17 cm. focusig circle; Philips Electronic Instruments, Type 42273/0). Approximately 1.5 meters of yarn are wound around a notched sample holder upon the bottom of which is cemented a sheet of lead foil across the rectangular hole so that the X-ray beam is diffracted only by the fibers on top of the hold. When the determination is made on staple fibers, the fibers are placed across the face of the sample holder and taped to each edge of the holder. Using CUKa radiation and 0.5 divergence and scatter slits, an equatorial intensity trace is recorded from 7 to 220, 20, at a scanning speed of 1, 20, per min., a chart speed of 1 inch (2.54 cm.) per min., and a time constant of l; 20 being the angle between the undilfracted beam and the diffracted beam. The full scale deflection of the recorder is set so that the peak with maximum intensity is at least 70% of the scale, which is a linear scale. The diffraction peak located at 11.5%, 20, is due entirely to diffracted radiation from the a crystal structure and is the maximum peak for samples of high a content. The diffraction peak located at approximately l7.8, 20, is due to diffracted radiation from both 0: and 8 crystal structure and is the maximum peak for the samples of high ,9 content. To calculate the a ratio, a base line is first established on the diffractometer scan by drawing a straight line between the points on the curve at 9.0 and 210, 20. Vertical lines are then drawn from points on the curve at and 164, 20, to the base line. FIG. 2 illustrates a typical diffractometer scan and the guide lines drawn on it for calculation of the a ratio. Using a planimeter, the area A of the diffraction peak between 9.0 and 13.5, 20, is measured and recorded. The area B of the diffraction peak Values for the a ratio as high as about 4.1 are observed, but for the purposes of the present invention should be 1.50 or less. Observed values for the a ratio can be as low as about 0.2.

The a crystallite size transverse to the fiber axis is the degree of order of a crystalline character, or apparent average width of ordered regions of a crystalline form, transverse to the fiber axis; simply stated, it is the average width of the a crystallites. It is determined from the same dilfractometer scan employed to calculate the a ratio, using the general method described by Klu g and Alexander in their book, X-ray Dilfraction Procedures, published by John Wiley & Sons, Inc., New York, 1954, pp. 491- 538. A vertical line is dropped from the peak in the vicinity of 11.5 20, to the base line, and the mid-point C of the line between the peak and the base line is ascertained. A horizontal line across the peak through C is drawn and the half-maximum pea-k breadth D is taken as the length of the horizontal line between its two intercepts on the curve, measured to the nearest 0.005 inch (.0127 cm.) and converted to degrees (1 inch 1 degree). The a crystallite size is then calculated from the equation H a. crystalllte S128, 14.:m where D=breadth at half-maximum peak height in degrees =the Bragg angle=5.75 H=wavelength of radiation 1.5418 A. where CuKot radiation is used I=breadth at Half-maximum peak height in degrees when calibrated by a metallic silicon standard (instrumental broadening) Values for the a crystallite size as high as 300 A. are observed, but for the purposes of the present invention should be less than 125 A. for stretch resistant fibers.

Observed values for the apparent at crystallite size can be as low as 30 A.

A measure of the degree of order of a crystalline character parallel to the fiber axis, or the apparent variation in the average length of ordered regions of a crystalline form in the direction of the axis, is given by the radial breadth of the low angle meridional X-ray peak, briefly designated herein as the radial breadth. The radial breadth is measured by making a low angle X-ray diffraction pattern (transmission pattern), using a camera of the type described by W. O. Statton for use in small angle studies and shown in FIGURE VI-l, page 233, of his chapter in the book, Never Methods of Polymer Characterization, edited by Bacon Ke and published by Interscience Publishers, New York, 1964, of a fiber sample 40 mils thick, perpendicular to the axis of the fibers using CuKa radiation collimated by two 15-mil pinholes spaced 6 inches apart, and a 32-cm. sample-tofilm distance. A radial photometer intensity trace of the discrete diffraction spots is made along the meridian at the rate of 1 centimeter of the chart paper for each millimeter of film. FIG. 3 illustrates a typical intensity trace, in which the diffraction spots are symmetrical. A vertical center line q is drawn between the peaks. The center line is conveniently established by folding the trace so that the centers of the diffraction spots are superimposed and then creasing the trace at the position which is centered between these two peaks. A straight base line is drawn beneath each peak. A vertical line is dropped from one peak to the base line and the mid-point K between the peak and the base line is ascertained, determined logarithmically if the intensity scale is logarithmic, as in FIG. 3. A horizontal line across the peak through K is drawn and the distance L in mm. from the creased center line to the nearest peak edge is measured and recorded. Also the distance M in mm. from the creased center line to the farther peak edge is measured and recorded. The corresponding diffraction angles 6 and 0 are calculated, and their difference yields a value for the radical breadth;

tan 6 =L/3200 tan 0 =M/3200 Radial breadth=0 -0 Measurements are repeated for the other peak, and the average value is reported as the radial breadth. If the discrete diffraction spots are not symmetrical, the distance N between the two peaks is measured in mm. The diffraction angle 0 is calculated and a value for the radial breadth is then calculated according to the following equations:

tan 0 =N/ 6400 Radial breadth=2(0 0 A second calculation is made, using the value for 0;; determined from the other peak, and the average value is reported as the radial breadth. Radial breadth values ranging up towards 1 may be observed in some samples, but in accordance with the present invention it has been found that 0.40 is a critical radial breadth upper limit for fiber structures exhibiting high resistance to stretch. Radial breadth values down to about 0.15 are observed. The radial breadth values determined in accordance with the method described above are reproducible to :.03 employing the instrumental settings described.

The orientation angle of the fiber is determined by the general method described -by Krimm and Tobolsky, Textile Research Journal, vol. 21, pp. 805-22 (1951). A wide angle X-ray diffraction'pattern (transmission pattern) of the fiber is made, using CuKu radiation, a fibersample thickness of 20 mils, a sample-tofilm distance of 2.2 cm., and an exposure time of 5 minutes. The fibers are aligned perpendicular to the X-ray beam. Crimped fibers are placed under sufficient tension to straighten the fibers, taking care not to impart additional orientation by drawing them. An azimuthal scan is made and the arc length in degrees at the half-maximum intensity of the first equatorial dilfraction spot, which is located at 20, is measured and taken as the orientation angle of the sample. As indicated above, the diffraction peak located at 11.5 29, is due entirely to diffracted radiation from the a crystal structure; therefore, the orientation angle measured by this technique is a measure of the orientation of the a crystallites. Since the intensity trace is an essentially Gaussian curve and the measurement is made at half-maximum intensity, the physical meaning of the orientation angle given by the determination is that approximately 77% of the a crystallites are aligned within this angle about the fiber axis.

As disclosed above, the orientation angle should be 17 or less for stretch resistant fibers. Decreasing orientation angles are indicative 'of increasing orientation of the polymer molecules in the fiber. Values as low as about 12 are observed.

FIG. 4a and 4b, although not intended to be taken as limitative, are proposed conformations of the polypivalolactone molecule in the a and p crystalline forms. In each case two full repeating structural units, plus certain adjacent groups, are shown. The repeat distance of 4.74 A. is close to that which would be expected (4.9 A.) for an extended planar zig-zag, and it is therefore hypothesized that in the p crystalline form of polypivalolactone the atoms comprising the main polymer chain lie substantially in a single plane, with only slight distortion. The 5.97 A. repeat distance observed in the ot-vrystalline form is too large to be accounted for by a single repeating structural unit, and for two repeating structural units to be compressed to this distance it appear that the polymer chain must be folded in some nonplanar manner, perhaps into a type of spiral configuration.

The term inherent viscosity, as used herein, is defined as the polymer property determined in accordance with the following relationship:

wherein the relative viscosity, is caculated by dividing the flow time in a capillary viscometer of a dilute solution of the polymer by the flow time for the pure solvent, trifluoroacetic acid. The concentration (c) used in the examples is 0.5 gram of polymer per 100 ml. of solution, and the measurements are made at 30 C. A decrease in the inherent viscosity of a polymer is frequently noted when the polymer is extruded at high temperature through capillary orifices to form fibers. It has been found that there is a minimum inherent viscosity requirement of 0.75, measured when the polymer is already in fiber form, for the fibers of this invention exhibiting high resistance to stretch.

By boiled off relaxed is meant a procedure comprising stapling the fibers between cheesecloth, boiling one half hour in water containing 0.1% commercial sodium loral sulfate (a mixture of C to C fatty alcohol sulfates), drying one hour in a forced air oven at 40 C., removing the cheesecloth and conditioning the fibers 16 hours at 70 F. and 65% relative humidity.

TR tensile recovery from 5% elongation, is a measure of the extent to which a fiber or yarn recovers its original length after being stretched, as determined from a stressstrain curve. In this test the sample is stretched at the rate of of its test length per minute until it has reached approximately 5% elongation, after which it is held at this elongation for 30 seconds and then allowed to retract at a controlled rate of 10% per minute, based on its original test length. The extension during elongation and the recovery during retraction are measured along the elongation axis. TR is then calculated as the percentage ratio of the amount of fiber retraction to the amount of its elongation.

WR work recovery from 5% elongation, is a measure of the freedom from permanent re-alignment of the polymer molecules following stretching of the fiber or yarn.

The ratio of the work done by the polymer molecules in attempting to return to their original alignment following stretching to a predetermined elongation to the work done on the sample during stretching is termed the work recovery. The work recovery is determined from the same stressstrain curve employed to measure the tensile recovery at 5% elongation. WR is calculated as the percentage ratio of the area under the controlled relaxation curve to the area under the stretching curve.

By the term polypivalolactone is meant a linear condensation polyester consisting essentially of recurring ester structural units of the formula Alternative names for the polyester include poly(hydroxypivalic acid), poly(B-oxypivaloyl), poly(2,2-dimethylhydracrylate), and poly(2,2-dimethyl 3 hydroxypropionic acid) or poly(2,2-dimethyl-3-oxypropionoyl). The polyester is readily prepared by the polymerization of hydroxypivalic acid or its esters as disclosed by Alderson in his US. Patent 2,658,055; or by the polymerization of pivalolactone, the intramolecular ester of hydroxypivalic acid, as disclosed by Reynolds and Vickers in their British Patent 766,347. In a typical procedure, g. of pivalolacetone is added to a refluxing mixture of 250 ml. of n-hexane, 2.5 ml. of ethyl alcohol, 0.25 g. of triethylenediamine, 0.025 g. of 2,2-bis(4-hydroxyphenyl)propane and 0.075 g. of finely divided TiO Refiuxing is continued, with stirring, for 4 hours, during which time the delustered polypivalolactone polymer precipitates from the boiling mixture. The solid polymer is subsequently filtered off from the hexane solvent. Other procedures for preparing equivalent polymer are described by Alderson and by Reynolds and Vickers in the references mentioned below.

As used herein, a fiber consisting essentially of polypivalolactone refers not only to fibers wherein the sole fiberforming polymeric constituent is polypivalolactone but also to fibers formed from certain copolymers as indicated below. Thus, copolymeric components may be present in amounts of up to about 30 mol percent so long as they do not prevent the fiber from assuming high orientation with the required crystalline character. At the upper amounts of copolymer component content, it is preferred that the copolymeric units be grouped in sequences alternating with long polypivalolactone sequences to form a segmented or block copolyester. As copolymer components, the lactones or hydroxy-acids are particularly suited and especially )8- propiolactones such as disclosed by Etienne and Fischer in French Patent 1,231,163. For example, copolymers consisting essentially of the following units -onras derived from copolymerization of pivalolactone and a,ct-diethylpropiolactone are herein contemplated. Other suitable copolymers are prepared from pivalolactone and up to 30 mol percent of 2-methyl-2-chloromethyl propiolactone, 2,2-di-n-propylpropiolactone or other similar comonomers. Other comonomers that do not materially detract from the properties of the polypivaloactone homopolymer are also suitable in the invention. Of course, conventional additives as dyes, pigment, stabilizers, etc. may be present in the fibers.

The following examples will serve to illustrate the scope of the invention; however, they are not intended to be limitative.

EXAMPLE I Molten polypivalolactone having an inherent viscosity of 1.80 is extruded at 272 C. from a spinneret containing 15 orifices, each 0.009 inch (.023 cm.) in diameter. The extruded filaments are passed through a vertical water quench tube continuously fed by water maintained at 78 C. from a funnel surmounting the tube and maintained full of water. The filaments are passed through a convergence guide and the yarn so formed is taken up by a roll at 800 y.p.m. (823 meters/min.) and then passed to a draw roll at 900 y.p.m. after which the yarn is wound up at 867 y.p.m. (791 meters/min). The inherent viscosity of the polymer comprising the yarn is 1.60. A sample of the drawn yarn wound taut on a bobbin is heated for 40 minutes in an oven at 170 C.

This yarn is drawn 1.70 over a 36-inch (92 cm.) hot plate at C. followed by drawing 1.04X over a hot plate at C. and then wound up on another bobbin. The yarn on the bobbin is heated in an oven at 170 C. for 40 minutes. X-ray analysis of this yarn shows it to have an a-ratio of 0.36, an a-crystallite size of 72A., a low angle radial breadth of 023, and an 11.5 orientation angle of 13. The yarn has a tenacity of 6.5 g.p.d., a breaking elongation of 14%, an initial modulus of 43 g.p.d., a T of 4.4 g.p.d., a work recovery at 5% elongation of 81%, and a tensile recovery at 5% elongation of 89%. On unrestrained boil-off in water for 30 minutes the yarn shrinks 5%. X-ray analysis of the boiled otf yarn shows it to have an a-ratio of 0.46, an a-crystallite size of 81 A., a low angle radial breadth of 0.23" and an 11.5 orientation angle of 13. The boiled off yarn has a tenacity of 6.1 g.p.d., a breaking elongation of 16%, an initial modulus of 32 g.p.d., a T of 2.0 g.p.d., a Work recovery at elongation of 61%, and a tensile recovery at 5% elongation of 80% EXAMPLE II Yarn prepared as in the first paragraph of Example I is drawn l.66 over a 12-inch (30 cm.) hot plate at 140 C. and wound up on a metal bobbin. The yarn on the bobbin is heated in an oven for 0.5 hour during which time the temperature is raised from 170 to 190 C.

X-ray analysis of this yarn shows it to have an u-ratio of 1.22, an a-crystallite size of 122 A., a low angle radial breadth of 0.22, and an l1.5 orientation angle of 17. The yarn has a tenacity of 4.5 g.p.d., a breaking elongation of 19%, an initial modulus of 27 g.p.d., and a T of 2.2 g.p.d. -On unrestrained boiled off in water for 30 minutes the yarn shrinks 0.7%; when heated unrestrained at 160 C. the yarn shrinks 4.2%.

X-ray analysis of the boiled oif yarn shows it to have an a-ratio of 1.27, an a-crystallite size of 123 A., a low angle radial breadth of .24, and an 11.5 orientation angle of 13. The boiled ofl yarn has a tenacity of 4.6 g.p.d., a breaking elongation of 31%, and initial modulus of 30 g.p.d., and T of 1.6 g.p.d.

EXAMPLE III Molten polypivalolactone having an inherent viscosity of 1.61 is extruded at 275 C. from a spinneret containing 15 orifices each 0.009 inch (.023 cm.) in diameter. The extruded filaments are passed through a vertical water quench tube continuously fed by water maintained at 7 C. from a cylindrical pan surmounting the tube and maintained full of water. The filaments are passed through a convergence guide and the yarn so formed is taken up by a roll at 900 y.p.m. (823 meters/min.) and then passed to a draw roll at 1171 y.p.m. (1070 meters/min.) after which the yarn is wound up. The inherent viscosity of the polymer comprising the yarn is 1.26. The yarn is heated relaxed for 5 minutes at 175 C.

X-ray analysis of this yarn shows it to have an a-ratio of 2.52, an a-crystallite size of 134 A., a low angle radial breadth of 0.41, and an 11.5 orientation angle of 15. The yarn has a tenacity of 3.8 g.p.d., a breaking elongation of 105%, an initial modulus of 2-6 g.p.d., a T, of 0.92 g.p.d., a work recovery at 5% elongation of 78%, and a tensile recovery at 5% elongation of 95%.

EXAMPLE IV Polypivalolactone having an inherent viscosity of 2.5 corresponding to a logarithmic viscosity number of 160 (1% solution at 25 C. in a 60/40 mixture of phenol and O-chlorophenol) is extruded at 265 C. from a spinneret having 15 orifices each 0.007 inch (.018 cm.) in diameter. The extruded filaments are quenched by passing them through air at room temperature; the spinning speed being 300 y.p.m. (274 meters/min). The spun filaments are drawn over a 125 C. hot pin and wound up. The draw ratio is 3.6x. The inherent viscosity of the polymer comprising the yarn is 1.44.

X-ray analysis of this yarn shows it to have an ix-ratio of 1.29, and d-crystallite size of 84 A., a low angle radial breadth of 0.45 and an l1.5 orientation angle of 17. The yarn has a tenacity of 4.04 g.p.d., a breaking elongation of 74%, an initial modulus of 27 g.p.d., a T of 1.14 g.p.d., a work recovery at 5% elongation of 74%, and a tensile recovery at 5% elongation of 92%.

A sample of the drawn yarn is boiled off relaxed in water for 30 minutes. X-ray analysis of the boiled 01f yarn shows it to have an a-ratio of 1.47 an u-crystallite size of 82 A., a low angle radial breadth of 042, and an 11.5 orientation angle of 21. The boiled 01f yarn has a tenacity of 3.8 g.p.d., a breaking elongation of 74%, an initial modulus of 32 g.p.d., a T, of 1.00 g.p.d., a work recovery at 5% elongation of 71%, and a tensile recovery at 5% elongation of 92%.

10 EXAMPLE V The yarn described in the first paragraph of Example I except that the 170 C. heat set was for 30 minutes in stead of 40 minutes is drawn 1.58 over 2 hot plates, the first at 140 C. and the second at 200 C. The drawn yarn is wound on a paper cone and heated in an oven at 160 C. for 10 minutes and then the temperature is increased over 30 minutes to 200 C. The yarn is boiled oif relaxed in water for 30 minutes.

X-ray analysis of this yarn shows it to have an aratio of 1.62, an a-crystallite size of 142 A., a low angle radial breadth of 023 and an 11.5 orientation angle of 15. The yarn has a tenacity of 5.1 g.p.d., a breaking elongation of 53%, an initial modulus of 27 g.p.d., and a T of 1.2 g.p.d.

EXAMPLE VLI Hydroxypivalic acid is polymerized to form a polymer having an inherent viscosity of 1.13. Filaments of the polymer are extruded at 250 C. and quenched in a bath of kerosene maintained at 15 C., the spinning speed being 300 y.p.m. The yarn is drawn 3.5X and wound up. The inherent viscosity of the polymer comprising the yarn is 0.81. The drawn yarn is boiled otf relaxed for 30 minutes in water.

X-ray analysis of the boiled oif yarn shows it to have an a-ratio of 2.13, an a-crystallite size of A., a low angle radial breadth of 068, and an 11.5 orientation angle of 24. The boiled off yarn has a tenacity of 2.3 g.p.d., a breaking elongation of 72%, an initial modulus of 28 g.p.d., a T of 0.82 g.p.d., a work recovery at 5% elongation of 71%, and a tensile recovery at 5% elongation of 89%.

EXAMPLE VII Polypivalolactone having an inherent viscosity of 1.61 and containing 0.1% TiO is extruded at 275 C. from a spinneret having 15 orifices each 0.009 inch in diameter. The extruded filaments are quenched by passing them through a cold water quench tube and formed into a yarn by passage through a convergence guide. The yarn is taken up by a feed roll operated at a peripheral speed of 900 y.p.m. passed to a draw roll at a draw ratio of 1.3X and then wound up. The inherent viscosity of the polymer comprising the yarn is 1.35.

The yarn has a tenacity of 5.3 g.p.d., a breaking elongation of 39%, an initial modulus of 71 g.p.d., a work recovery at 5% elongation of 44%, and a tensile recovery at 5% elongation of 72%. X-ray analysis of the yarn shows it to have an u-ratio of 0.19 an a-crystallite size of 33 A. and an orientation angle at 11.5 of 16. The X-ray pattern for low angle radial breadth is too faint to be measured indicating low long range order of the a-crystallites parallel to the fiber axis.

The yarn is boiled otf relaxed for /2 hr. in 'water. The tenacity is 3.9 g.p.d., the breaking elongation 97%, the initial modulus 29 g.p.d., the work recovery at 5% elongation 69%, and the tensile recovery at 5% elongation X-ray analysis of the boiled off yarn shows it to have an a-ratio of 2.26, an a-crystallite size of 82 A., a low angle radial breadth of 0.59 and an 11.5 orientation angle of 21.

EXAMPLE VIII 200 ml. of benzene is refluxed in a 3-neck flask equipped with a stirrer and condenser. 5 mls. of a 0.1 N solution of the tetrabutylammonium salt of hexyldimethylacetic acid (mixture of 0 -0 trialkyl acetic acid available commercially as versatic acid from Shell Chemical Co.) in benzene is added. To this is added 25.6 g. (0.2 mole) diethylpropiolactone followed by a 20 ml. benzene rinse. After 30 minutes at reflux, an additional 700 ml. benzene is added and the mixture brought back to a boil. Pivalolactone (80.0 g.) is added followed by a 20 ml. benzene rinse. The mixture is heated under reflux with stirring for 2 hrs. When cool, methanol is added to coagulate the copolymer which is removed by filtration, washed with methanol and dried in a vacuum oven at 80 C. The copolymer has an inherent viscosity as measured in trifiuoroacetic acid of 1.65. 2,6-di-t-butyl-p-cresol (1.5%) is added from an acetone solution and the polymer redried.

The molten copolymer is extruded from a spinneret having 15 orifices 0.009 inch (.023 cm.) in diameter. The extruded filaments are passed through a vertical waterquench tube continuously fed by Water maintained at C. from a cylindrical pan surmounting the tube and maintained full of water. The filaments are passed through a convergence guide and the yarn wound up at 500 y.p.m. (457 meters/min.). The yarn is drawn 2.05 X at 185 C. over a hot plate. The drawn yarn is heat set on a paper cone by heating 1 hr. at 125 C. and 16 hrs. at 175 C. The heat set yarn is boiled ofi? relaxed in water for /2 hr. X-ray analysis of the boiled off yarn shows it to have an a-ratio of 1.88, an a-crystallite size of 113 A., and an 11.5 orientation angle of 16. The boiled 01f yarn has a tenacity of 4.6 g.p.d., a breaking elongation of 64%, an initial modulus of 46 g.p.d., and a T of 1.3

g.p.d.

EXAMPLE IX A copolymer having an inherent viscosity of 1.60 is prepared following the procedure of the preceding example. This copolymer is press spun at 252 C. through a single orifice 0.012 inch (.030 cm.) in diameter. The extruded filament is passed through a vertical water quench tube continuously fed by water maintained at 6 C. from a cylindrical pan surmounting the tube and maintained full of water. The filament is wound up at 500 yds./min. (457 meters/min). The filament is drawn 2.3 X over a hot plate at 180 C. followed by a draw of 1.25 x over a hot plate at 190 C. The drawn filament is heat set on an aluminum bobbin by heating 1 hr. at 125 C. and 18 hrs. at 170 C. The drawn filament is boiled off relaxed in water for /2 hr. X-ray analysis of the boiled oif filament indicates an u-ratio of 1.02, an acrystallite size of 78 A., and an 11.5 orientation angle of 14. The filaments have a tenacity of 6.1 g.p.d., a breaking elongation of 14%, an initial modulus of 62 g.p.d., and a T of 4.1 g.p.d.

What is claimed is:

1. A process for preparing fibers having a T of at least 1.5 grams per denier after boil-01f comprising heating an oriented fiber whose orientation angle has a numerical value of less than 8 15 and which consists essentially of polypivalolactone having an inherent viscosity of at least 0.75, to a temperature of at least C. for at least three seconds, drawing the fiber at least 1.5x at a temperature in the range of 120 C. to 190 C. and heat setting the fiber at a temperature in the range of C. to 200 C.

References Cited UNITED STATES PATENTS 3,361,859 1/1968 Cenzato 264-210 F 3,366,597 1/1968 FOl't 260-40 P 3,418,393 12/1968 King 260-857 PE 3,432,590 3/1969 Papps 264-210 F 3,513,110 5/1970 Noether 264-210 F 3,551,363 12/1970 Brody 264-342 RE 3,560,604 2/1971 Papps 264-168 3,575,907 4/1971 Kitazawa et al. 264-2l0 F 3,608,295 9/1971 Kitazawa 57-157 R 2,807,863 10/ 1957 Schenker 264-290 N 2,948,583 8/1960 Adams et a1. 264-210 F 3,107,140 10/ 1963 Kurzke et al. 264-290 3,423,501 1/1969 Dennis et al 264-290 X 3,426,754 2/1969 Biernbaum et a1. 128-156 3,469,001 9/ 1969 Keefe 264-290 3,215,486 11/1965 Hada et al. 264-210 FX 3,256,258 6/1966 Herrman 264-210 FX 3,323,190 6/1967 Boltniew 264-176 FUX 3,345,343 10/1967 Tietz 260-783 3,379,001 4/1968 Campbell 161-169 X 3,030,173 4/1962 Kurzke et al 264-210 F 3,299,171 1/1967 Knoblock et a1. 260-783 FOREIGN PATENTS 893,494 4/1962 Great Britain 264-210 JAY H. WOO, Primary Examiner U.S. Cl. X.R. 

